The present invention relates to a steel roll for metal rolling, more specifically to a roll for forming irregularities on a surface of an aluminum plate by embossing and to a support for a lithographic printing plate obtained by use of the roll.
In a method of manufacturing a support for a lithographic printing plate by forming irregularities on a surface of an aluminum plate by embossing or the like with a steel roll provided with irregularities in advance, a roll for metal rolling formed by shot-blasting the surface of the steel roll has been known (JP 60-36196 A). There are also disclosed other related methods, namely, a rolling method using a steel roll fabricated by honing (forming 500 pieces/mm2 or more irregularities each having an Ra of 0.5 to 1.5 μm and a depth of 0.6 μm or above) while applying a draft of 2% to 20% (JP 62-25094 A), a rolling method using a roll fabricated by chemical etching or honing so as to form 500 pieces/mm2 or more irregularities each having an Ra of 0.5 to 1.5 μm and a depth of 0.6 μm or above while applying a draft of 2% to 20% (JP 62-111792 A), and a rolling method using a roll fabricated by electric discharge machining (forming 500 pieces/mm2 or more irregularities each having an Ra of 0.7 to 1.7 μm and a depth of 0.6 μm or above) while applying a draft of 2% to 20% (JP 62-218189 A).
Concerning the surface of the roll for metal rolling, the conventional techniques have proved that the life duration of the roll is enhanced by regulating positions of peaks of the irregularities formed on the surface of the roll (such positions may be hereinafter referred to as “levels of peaks on the roll surface” when appropriate). However, the conventional roll for rolling an aluminum plate for a support for a lithographic printing plate has been formed with a roughened surface by hitting the surface with abrasives through blasting such as air blasting or shot blasting. Accordingly, the levels of the peaks on the roll surface tended to be uneven. In this way, it has been difficult to obtain the roll surface having desired irregularities sufficient for embossing, and having sufficiently regulated levels of the peaks on the roll surface.
Meanwhile, by use of the rolls according to the conventional techniques, it has been difficult to obtain an aluminum support formed by providing an aluminum plate with irregularities using the roll, which has excellent printing performances particularly in the number of printed sheets, sensitivity, stain resistance, and ink spread resistance when formed into an aluminum support for a lithographic printing plate or more specifically an aluminum support for a CTP plate (which stands for the computer-to-plate technique for manufacturing a lithographic printing plate directly without using a lithographic film by scanning and exposing a presensitized plate to highly convergent radiant rays such as laser beams carrying digitalized image information).
Meanwhile, as a surface roughening method for a surface of a stainless steel plate, a method of obtaining a stainless steel plate having excellent adhesion to various covering materials by performing an alternating current electrolysis in a ferric chloride aqueous solution has been known (JP 10-259499 A).
As another surface roughening method for a surface of a stainless steel plate, a method of obtaining a non-glaring surface-roughened stainless steel plate with small luminosity direction dependency by performing an alternating current electrolysis in a ferric chloride aqueous solution has also been known (JP 11-61354 A).
As still another surface roughening method for a surface of a stainless steel plate, a Cu—Ni alloy covered stainless steel plate obtained by performing Ni plating and Cu plating on a roughened surface formed by performing an alterating current electrolysis in a ferric chloride aqueous solution has also been known (JP 11-61377 A).
In addition, there has also been known a surface roughening method for enhancing adhesion of a steel plate to coating films or adhesives which includes performing an anodic electrolysis for surface roughening by using a steel plate other than stainless steel such as ordinary steel or special steel as an anodic electrode and applying current density in a range of 50 to 150 A/dm2 while generating oxygen bubbles on a steel surface (JP 2003-3300 A).
As a roll for metal rolling for a process used in rolling a steel plate or the like, there has been known a chromium-plated roll for metal rolling formed by performing an electrolytic treatment using a dull finished roll as an anode in an electrolytic solution and thereby increasing the number of peaks on a surface of the roll by 1% to 50% as many as the number of peaks before the electrolysis (JP 64-8293 A).
There have also been known a chromium-plated roll for metal rolling formed by reducing surface roughness in terms of Rz by 5% to 20% as compared to initial roughness before or after chromium plating (JP 61-202707 A), a chromium-plated roll formed by plating chromium using a chromium plating solution including chromic anhydride and sulfuric acid while using the roll as an anode in an etching treatment, which is performed after reducing surface roughness in terms of Rz by 5% to 20% as compared to initial roughness (JP 61-201800 A), and a chromium-plated roll formed by performing a electrolytic treatment in a chromium plating solution while using a bright finish roll as an anode, increasing the number of peaks on a surface of the roll represented by peaks per inch (PPI) by 1.3 to 15 times as many as the initial number of peaks, performing chromium plating while using the roll as a cathode, and then polishing the surface of the plated roll (JP 1-123094 A).
Meanwhile, as a method of manufacturing a chromium-plated roll, there has been known a method including the steps of performing an electrolytic treatment in an electrolytic solution while using a roll base material as an anode, and then performing chromium plating in a chromium plating bath having Fe concentration less than 5 g/dm3, by increasing current density from 0 to 25-35 A/dm2 in a time period of 10 to 30 minutes while using the roll base material as a cathode, maintaining the current density for 2 to 3 minutes, and then reducing and retaining the current density to 20-30 A/dm2 (JP 2001-240994 A), for example.
In these rolls, the surface of the steel roll before the chromium plating may be subjected to an etching treatment so as to enhance adhesion to a chromium-plated layer. However, the roll used for rolling steel plates and the like includes the chromium-plated surface which is configured to roll and finish a cold-rolled steel plate smoothly irrespective of whether the roll is formed as a roll for highly smooth bright steel plates or as a roll for appropriately roughened dull steel plates. Accordingly, an intended shape of a surface of an end product is completely different as compared to a transfer roll for embossing.
In addition, in terms of the rolls for metal rolling, the methods of manufacturing the roll for metal rolling, manufacturing devices, and plating devices, various techniques have been known as disclosed in JP 7-180084 A (a plating device), JP 63-99166 A (a mirror surface polishing device), JP 8-27594 A (a method of manufacturing a steel plate and a chromium-plated roll therefor), JP 5-65686 A (a method of manufacturing a dull roll for metal rolling), JP 2003-171799 A (a batchwise chromium plating method and equipment), JP 3-47985 A (a chromium plating method), JP 2002-47595 A (a chromium plating method and a chromium plating apparatus), and the like.